You can make a complaint about almost anything.
Most people want to make a complaint because they have been wrongly arrested, assaulted by the police or prosecuted for something they didn’t do, and make it in parallel with a civil claim.
You are additionally able make a complaint about unprofessional conduct and rudeness.
Unlawful arrest and detention is called false imprisonment. The police must justify any arrest and detention, so if you think the police have acted outside their powers it is worthwhile getting further advice. False imprisonment can happen on the street, in your home, in a police vehicle and of course at the police station – in fact any place where the police control your freedom.
This is much wider than many people think. You are assaulted as soon as someone touches you without a lawful reason to do so, and when they put you in fear of unlawful violence. Of course, it includes being punched and kicked and being subjected to illegal body searches. If you are assaulted by the police it is important to see a doctor (at casualty or your GP) straight away and for the injuries to be noted. You should also take photos of any injuries, if possible.
Prosecuted for something I didn’t do
This is called malicious prosecution. You have to prove that the police had no reasonable cause to prosecute you and that they had a “wrongful motive” in doing so. You have to win your criminal case, which means either (a) any charges were dropped before the case went to court, or , or (b) you were acquitted (found innocent) in court at your trial or on appeal.
You can also sue the police for breach of your right to protest or breach of other human right; negligence; trespass to land and goods; breach of your rights under the Data Protection Act; race, sex, disability or other discrimination; and a few other civil wrongs.